TIME HISTORY FATIGUE ANALYSIS IN SACS

Hello All,

Greetings.

I have to perform TIME HISTORY FATIGUE ANALYSIS IN SACS, for some project as per the client requirement. I have experience in doing deterministic and spectral fatigue analysis, but time history domain is completely new to me. I have gone through the sacs wave response module and some other papers dealing with time history fatigue and got some insight regarding that but still very vague in how to perform the analysis in sacs (Procedures).

1) how to decide the time increment?

2) what is the number of frequencies to be considered & where it is going as the input in the analysis?

3) what is seed means and how to decide the number of seeds?

4) what is the time duration to be considered? ( for fixed offshore well head jacket structures)

5) How sacs will perform the Rain flow counting process?

6) What is the Return period (like 1-yr or 10-yr or 100-yr) to be considered for the Significant wave height and Dominant period?

Kindly provide me a sample time history fatigue sacs file with procedure so that I can complete my task within stipulated time. Also if permits provide me the step by step procedure write up (denoting how the input flows and the corresponding output) and some theoretical backup calculation references.

Thanks & Regards,

Vasudevan V

Structural Engineer - Offshore.

Parents
  • Hi,

    Are you trying to run time history fatigue from a random wave? Are you trying to generate the random wave from a wave spectrum or self-defined surface profile?  Normally for jacket wave fatigue analysis we use spectral method as the time history method would cost numerous analysis time.

    For your question,

    1 & 4, For a time history simulation of wave, definitely the time increment should be small enough and the time duration should be long enough to reflect the random characteristic of wave. This is usually determined by engineers themselves and you can refer to the design code required to follow by your project.

    2 & 6, For both spectral and time history wave fatigue, I guess you need the same wave scatter diagram which includes the probabilities of different wave spectrums from different direction. For each wave spectrum in scatter diagram you should make a time history simulation and run a time history fatigue. Then the total damage is accumulated for each time history simulation.

    3, Please check 3.1.2~4 of  "wind turbine" manual for the random wave surface generation. Each seed will generate a different surface and user should determine how many seeds shall be calculated and which one to be used.

    5, SACS time history fatigue use rainflow method(ASTM E 1049-85,Standard practices for cycle counting in fatigue analysis,Reapproved 2005) to count for cyclic stress and number of occurrence. If you want to know details, please review that reference.

    However, all these can be found in SACS wave response and fatigue manual and I can send you a simple sample of single time history.

  • Hi Wen Meng,

    I am Rizqi. I am doing my thesis about wind turbine fatigue analysis which would need time history fatigue analysis in SACS.

    Would you mind sending me a simple sample of single time history sacs file, please? 

    Thank you very much,

    Rizqi Widya A.

  • Please let me know your email address so that I can send the sample file,

Reply Children
No Data